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Wednesday, September 20, 2006

On Sunday I attended the DC Audubon Society's annual September field trip to Rock Creek Park. For those not familiar with the area, Rock Creek Park is the hotspot for migratory songbirds in Washington, DC. Picnic areas 17/18 on Glover Road and the maintenance yard are particularly productive.

On Sunday, the most common neotropical migrant was probably the red-eyed vireo. Every tangle of vines, every tree, and every bush seemed to have a red-eyed vireo hopping in and out of the foliage. Other birders estimated that there were about 30 red-eyed vireos around the ridge, maintenance yard, and nature center that day.

Red-eyed Vireo / Painting by Louis Agassiz Fuertes

Red-eyed vireos reported in D.C. during the fall are a mixture of local breeders and migrants from up north. This species breeds as far north as the Yukon Territories in western Canada; in the east it ranges up to the southern half of Ontario and Quebec. In the mid-Atlantic, red-eyed vireos are widespread and common breeders. Throughout the summer one can hear their simple three-syllable songs echoing from high in the canopy. Even in the middle of the day, red-eyed vireos will keep singing: "Here I am. In the tree. At the top. Can't see me." All red-eyed vireos, whether they bred in D.C. or farther north, are on their way south to their wintering grounds in northern South America.

In the flurry of drab birds that make up fall migration, it is helpful to be able to recognize red-eyed vireos. Being able to confirm or eliminate red-eyed vireo quickly will help one to pick out other, less common, migrant species that share the red-eyed vireo's drab coloration. Within the vireo family, warbling vireo and Philadelphia vireo are superficially similar in their facial markings and drab backs. However, the eyebrow and eyeline of both species are far less bold than on a red-eyed vireo. A warbling vireo tends to be browner than a red-eyed vireo's olive-green back. Philadelphia vireos have clearly yellow throats and undersides, as well as a shorter tail.

Outside of the vireo family, red-eyed vireos may be confused with Tennessee warblers. Like red-eyed vireos, Tennessee warblers show gray heads, olive backs, and light undersides. However, one can usually tell the difference by the bill, which is hooked for vireos but straight and sharp for warblers. In addition, while Tennessee warblers have white eyebrows, they lack the bold black eyeline that distinguishes red-eyed vireos. Tennessee warblers also have shorter tails.

Get out and enjoy the challenge of fall migration while it is with us. Several species pass through in good numbers at this time but not at others. A cold front has just passed through the D.C. area, and we are sure to get a few more before all the warblers have passed. But time is short; by mid-October most of the warblers, and the red-eyed vireos, will be gone until next spring.